<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    /* 
    设计稿的宽度  375
    设计稿中div   100 * 100
    手机屏幕的宽  100vw

     */
    div {
      /* width: 100px; */

      width: calc(100vw * 100 / 375);
      height: calc(100vw * 100 / 375);
      background-color: sandybrown;
    }
  </style>
</head>

<body>
  <div></div>
</body>

</html>